1. Field of the Invention
The present invention relates to a driving device and a light amount adjusting device using the driving device, and more particularly, to a driving device having a reduced size in the direction of rotor rotation axis and a light amount adjusting device utilized in a shutter mechanism, an aperture control mechanism, and the like, in which the driving device is used as a drive source thereof.
2. Description of the Related Art
Conventionally, as a light amount adjusting device for adjusting the amount of exposure in image pickup devices such as a camera and a video camera, there has been proposed a flat actuator which is small in size in the thickness direction thereof (see Japanese Laid-open Patent Publication (Kokai) No. 2004-045682, for example).
FIG. 10 is an exploded perspective view showing the component parts of the prior art light amount adjusting device disclosed in Japanese Laid-open Patent Publication (Kokai) No. 2004-045682. FIG. 11 is a sectional view showing the structure of the light amount adjusting device in an assembled state.
As shown in FIGS. 10 and 11, the light amount adjusting device is comprised of a driving device and a light amount control mechanism, wherein the driving device includes a rotor magnet 101, a coil 102, a first stator 103, and a second stator 104, whereas the light amount control mechanism includes a base plate 105, a front base plate 106, and a plurality of shutter blades 107.
The rotor magnet 101 is formed into a hollow circular disk shape and held by the base plate 105 for rotation about the center of the circular disk. The rotor magnet 101 has a face extending perpendicular to the center axis thereof and circumferentially divided into areas that are alternately magnetized into different poles. The coil 102 is formed into an annular circular shape, is disposed coaxially with the rotor magnet 101, and is arranged to have an inner peripheral face thereof facing an outer peripheral face of the rotor magnet 101. The first and second stators 103, 104 each have tooth shaped magnetic pole parts extending radially inward. These magnetic pole parts are opposed to the magnetized surface of the rotor magnet 101.
When the coil is supplied with electric power, each of the magnetic pole parts of the first and second stators 103 and 104 is magnetized into an N or S pole, whereby the rotor magnet 101 is rotated reciprocally within a limited range. With the rotation of the rotor magnet 101, the shutter blades 107 are opened or closed, whereby the open area amount of an opening part 106a provided in the front base pale 106 can be adjusted. At this time, the magnetic flux generated by power supply to the coil 102 flows from the magnetic pole parts of the first stator 103 to those of the second stator 104 or flows in the opposite direction, thereby effectively acting on the rotor magnet 101 disposed between these stators 103 and 104. As a result, a small-sized efficient actuator is realized.
In the aforesaid light amount adjusting device, the size of the driving device in the thickness (axial) direction is equal to the sum of the thicknesses of the first stator, the second stator, and the rotor magnet, and a value twice as large as the clearance between the rotor magnet and each of the first and second stators. Thus, the driving device that is thin in the thickness direction can be realized to some extent.
However, with the light amount adjusting device disclosed in Japanese Laid-open Patent Publication (Kokai) No. 2004-045682, the component parts (the magnetic pole parts of the first and second stators and the rotor magnet) of the driving device and the component parts (the shutter blades) of the light amount control mechanism are juxtaposed to one another in the direction of the rotation axis. Thus, the total thickness of the light amount adjusting device is larger than the sum of the thicknesses of these component parts, making it difficult to make the light amount adjusting device thinner.